Alloy type semiconductor nanocrystals and method for preparing the same

ABSTRACT

Provided is a chemical wet preparation method for Group 12-16 compound semiconductor nanocrystals. The method includes mixing one or more Group 12 metals or Group 12 precursors with a dispersing agent and a solvent followed by heating to obtain a Group 12 metal precursor solution; dissolving one or more Group 16 elements or Group 16 precursors in a coordinating solvent to obtain a Group 16 element precursor solution; and mixing the Group 12 metal precursors solution and the Group 16 element precursors solution to form a mixture, and then reacting the mixture to grow the semiconductor nanocrystals. The Group 12-16 compound semiconductor nanocrystals are stable and have high quantum efficiency and uniform sizes and shapes.

BACKGROUND OF THE INVENTION

This application claims priority from Korean Patent Application No.2003-49547, filed on Jul. 19, 2003, in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein in its entiretyby reference.

1. Field of the Invention

The present invention relates to alloy type semiconductor nanocrystalsand a method of preparing the same. More particularly, the presentinvention relates to alloy type Group 12-16 compound semiconductornanocrystals with a high luminance efficiency in a visible light bandand a wet preparation method for the semiconductor nanocrystals.

2. Description of the Related Art

When compound semiconductor materials are made into nanometer-sizedcrystals, a quantum confinement effect occurs at the regions of thecrystals smaller than the bulk exciton Bohr radius. Such a quantumconfinement effect results in a change in bandgap energy which isintrinsic characteristics of semiconductor materials. In a case wherevisible light-emitting compound semiconductor materials are made intonanocrystals, a bandgap energy commences to increase when the size ofthe nanocrystals reaches below a specific level. As a result, thesmaller sized nanocrystals exhibit a blue shift of a luminance band.Based on such size-dependent optical characteristics of quantum dotmaterials, adjustments of intrinsic properties, structures, shapes, andsizes of the quantum dot materials enable a change in an energy bandgap,which allows formation of various energy levels.

Studies have been done on a quantum dot growth technology as the mostimportant technology among next generation semiconductor devicedevelopment technologies. In particular, metal organic chemicaldeposition (MOCVD) and molecular beam epitaxy (MBE) which areconventional vapor phase deposition processes are promising technologieswhich allow a control of a semiconductor thin film to a single atomiclayer level and a controllable growth of quantum dots. Even thoughquantum dots grown mainly by lattice mismatch using a vapor phase methodhave good crystallinity, the vapor phase method has a fatal defect incontrolling the size, uniformity, and density of the quantum dots, whichrenders fabrication of commercially available semiconductor devicesdifficult.

In view of these problems, there was an attempt to grow quantum dotsusing a chemical wet method. According to the chemical wet method,quantum dot crystal precursor materials grow into quantum dot crystalsin a coordinating organic solvent. The organic solvent spontaneouslycoordinates with the surfaces of the quantum dot crystals. At this time,the organic solvent serves as a dispersing agent to control the size ofthe quantum dot crystals to a nanometer level.

U.S. Pat. No. 6,225,198 B1 discloses a method for forming Group 12-16compound semiconductor quantum dots. According to the method disclosedin this patent, a Group 12 metal (Zn, Cd, or Hg) containing materialwhich is a Group 12 precursor is dissolved in a first dispersion and aGroup 16 element (S, Se, or Te) containing material which is a Group 16precursor is dissolved in a second dispersion. A solvent capable ofdissolving the two precursors is added to a mixture of the twodispersions and maintained at a temperature sufficient to promote thegrowth of Group 12-16 compound semiconductor crystals. When the sizes ofthe compound semiconductor crystals reach a desired level, the crystalsare separated. However, this method has a restriction on the solventused, i.e., tri-octyl phophonic acid (referred to as TOPO, hereinafter).TOPO is commercially available only as technical grade (about 90% pure)TOPO. Reportedly, it is difficult to form reproducible and uniformquantum structures in a solvent containing a large amount of impurities.It is also reported that impurities in the technical grade TOPO servesas an uncontrollable reaction parameter that adversely affects thereaction. In this regard, substitution of pure (99%) TOPO for thetechnical grade TOPO can be considered. In this case, however, a changein a binding property of TOPO may occur, which renders the growth ofdesired crystals difficult.

U.S. Pat. No. 6,306,736 discloses a method for forming Group 3-5compound semiconductor quantum dots. Here, the above-described methodfor forming Group 12-16 compound semiconductor quantum dots is used asit is.

U.S. Pat. No. 6,322,901B1 discloses high-luminescent core-shell quantumdot materials and U.S. Pat. No. 6,207,229 discloses a method forpreparing core-shell quantum dot materials. It is reported that thecore-shell compound semiconductor quantum dots thus formed exhibit anincrease in luminance efficiency by 30 to 50%.

SUMMARY OF THE INVENTION

The present invention provides alloy type Group 12-16 compoundsemiconductor nanocrystals which are stable and have a high quantumefficiency and uniform sizes and shapes.

The present invention also provides a simple, reproducible, chemical wetpreparation method for the alloy type Group 12-16 compound semiconductornanocrystals.

The present invention also provides an organic electroluminescent (EL)device with good luminance characteristics using the Group 12-16compound semiconductor nanocrystals.

According to an aspect of the present invention, there is provided amethod for preparing semiconductor nanocrystals including: (a) mixingone or more Group 12 metals or Group 12 precursors with a dispersingagent and a solvent followed by heating to obtain a Group 12 metalprecursor solution; (b) dissolving one or more Group 16 elements orGroup 16 precursors in a coordinating solvent to obtain a Group 16element precursor solution; and (c) mixing the Group 12 metal precursorssolution and the Group 16 element precursors solution to form a mixture,and then reacting the mixture to grow the semiconductor nanocrystals.

According to another aspect of the present invention, there is providedsemiconductor nanocrystals having three or more component alloy quantumstructures comprised of one or more Group 12 metals and one or moreGroup 16 elements. The semiconductor nanocrystals may be ZnSSe, ZnSeTe,ZnSTe, CdSSe, CdSeTe, CdSTe, HgSSe, HgSeTe, HgSTe, ZnCdS, ZnCdSe,ZnCdTe, ZnHgS, ZnHgSe, ZnHgTe, CdHgS, CdHgSe, CdHgTe, ZnCdSSe, ZnHgSSe,ZnCdSeTe, ZnHgSeTe, CdHgSSe, or CdHgSeTe.

According to yet another aspect of the present invention, there isprovided an organic EL device including an organic film interposedbetween a pair of electrodes, the organic film including theabove-described semiconductor nanocrystals.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a high resolution, transmission electron microscopic (TEM)image (scale bar=5 nm) of CdSeS nanocrystals according to Example 5 ofthe present invention;

FIG. 2 is a scanning transmission electron microscopic (STEM)/energydispersive spectrometric (EDS) image (scale bar=50 nm) of the CdSeSnanocrystals according to Example 5 of the present invention;

FIG. 3 is a X-ray diffraction spectrum of the CdSeS nanocrystalsaccording to Example 5 of the present invention;

FIG. 4 is an ultraviolet absorption spectrum of the CdSeS nanocrystalsaccording to Example 5 of the present invention;

FIG. 5 is a photoluminescence (PL) spectrum of the CdSeS nanocrystals,ZnCdSe nanocrystals, and CdSe/CdS nanocrystals according to Examples 1-3of the present invention; and

FIG. 6 is an EL spectrum of an organic EL device according to Example 4.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method for preparing semiconductornanocrystals which includes: mixing at least one Group 12metal/precursor with a dispersing agent and a solvent followed byheating at a predetermined temperature to obtain a uniform solution;dissolving at least one Group 16 element/precursor in an appropriatecoordinating solvent; and mixing the solution containing the Group 16element/precursor with the solution containing the Group 12metal/precursor that has been maintained at a predetermined temperatureto grow the semiconductor nanocrystals. The semiconductor nanocrystalsprepared through this simple process have Group 12-16 compoundsemiconductor quantum structures with a very narrow size distribution(full width at half maximum (FWHM) <30 nm), high luminance efficiency(>50%), and good reproducibility. In particular, three or more componentcompound semiconductor quantum dots have excellent crystallinity. Also,uniform compound semiconductor quantum dots can be obtained without aselective separation process.

Three or more component compound semiconductor nanocrystals can beprepared by dissolving at least one Group 12 metal/precursor in asolvent and a dispersing agent to obtain a Group 12 metal precursorsolution, and adding two or more Group 16 element precursor solutionsobtained by dissolving two or more Group 16 elements/precursors in asolvent to the Group 12 metal precursor solution, in sequence or at atime. The compound semiconductor nanocrystals can have a specificcrystal structure according to a reaction rate difference and a mixtureratio between different elements. Furthermore, the compoundsemiconductor nanocrystals can have specific bandgap and luminanceefficiency according to the types of the used elements or precursors.

A method for preparing semiconductor nanocrystals according to thepresent invention will now be described in detail.

First, at least one Group 12 metal/precursor is mixed with a dispersingagent and a solvent and heated at a predetermined temperature to obtaina Group 12 metal precursor solution.

The Group 12 metal may be Zn, Cd, Hg, or a mixture thereof. The Group 12precursor is a material that is relatively stable in air and does notgenerate noxious gases during addition of the precursor, for example, aGroup 12 metal oxide, a Group 12 metal halide, or a Group 12 metalorganic complex. Examples of the Group 12 precursor include zincacetate, zinc acetylacetonate, zinc iodide, zinc bromide, zinc chloride,zinc fluoride, zinc carbonate, zinc cyanide, zinc nitrate, zinc oxide,zinc peroxide, zinc perchlorate, zinc sulfate, cadmium acetate, cadmiumacetylacetonate, cadmium iodide, cadmium bromide, cadmium chloride,cadmium fluoride, cadmium carbonate, cadmium nitrate, cadmium oxide,cadmium perchlorate, cadmium phosphide, cadmium sulfate, mercuryacetate, mercury iodide, mercury bromide, mercury chloride, mercuryfluoride, mercury cyanide, mercury nitrate, mercury oxide, mercuryperchlorate, mercury sulfate, and a mixture thereof.

The dispersing agent as used herein is a material that reacts with theGroup 12 metal/precursor to form a Group 12 metal complex. Thecoordinating capacity of the dispersing agent and the growth rate on aspecific crystalline surface can vary according to the type andconcentration of the dispersing agent. Therefore, the dispersing agentis a factor that has an important effect on the sizes and shapes ofsemiconductor nanocrystals to be finally obtained.

The dispersing agent may be a weakly acidic organic material, forexample, an alkylcarboxylic acid having from 2 to 18 carbon atoms with aCOOH end group, an alkenylcarboxylic acid having from 2 to 18 carbonatoms with a PO₃H end group, an alkylsulfonic acid having from 2 to 18carbon atoms with a SO₃H end group, or an alkenylsulfonic acid havingfrom 2 to 18 carbon atoms. The dispersing agent may also be a weaklybasic organic material, for example, an alkylamine having from 2 to 18carbon atoms with a NH₂ end group or an alkenylamine having from 2 to 18carbon atoms with a NH₂ end group. Examples of the dispersing agentinclude oleic acid, stearic acid, palmitic acid, hexyl phophonic acid,n-octyl phosphonic acid, tetradecyl phosphonic acid, octadecylphosphonic acid, n-octyl amine, and hexyldecyl amine.

Preferably, the molar ratio of the Group 12 metal/precursor to thedispersing agent is in a range of 1:0.1 to 1:100, more preferably, 1:1to 1:20, still more preferably, 1:2 to 1:8. If the molar ratio of thedispersing agent is less than 0.1, the Group 12 metal/precursor may beunstable. On the other hand, if it exceeds 100, control of a reactionrate may be difficult and nanocrystals may have a broad sizedistribution.

The solvent as used herein is a solvent that contains a lesser amount ofimpurities, is in a liquid state at room temperature, and has anappropriate coordinating capacity. The solvent may be a primary alkylamine having from 6 to 22 carbon atoms, a secondary alkyl amine havingfrom 6 to 22 carbon atoms, a tertiary alkyl amine having from 6 to 22carbon atoms, a nitrogen-containing hetero ring compound having from 6to 22 carbon atoms, a sulfur-containing hetero ring compound having from6 to 22 carbon atoms, an alkane having from 6 to 22 carbon atoms, analkene having from 6 to 22 carbon atoms, or an alkyne having from 6 to22 carbon atoms. Examples of the primary alkyl amine includedodecylamine, hexadecylamine, and dimethyldodecylamine. The secondaryalkyl amine may be dioctylamine and the tertiary alkyl amine may betrioctylamine. The nitrogen-containing hetero ring compound may beisopropyl-2,3-diphenylaziridine, the sulfur-containing hetero ringcompound may be dimethylsulfolane, the alkane may be octadecane, thealkene may be octadecene, and the alkyne may be dodecyne.

The solvent must have an appropriate coordinating capacity andcrystalline nuclei dispersability and, at the same time, be stable at ahigh reaction temperature. In this regard, the solvent may havecarbon-carbon bonds of more than a predetermined length, and the solventhave preferably 6-18 carbon atoms. The solvent must havesolubilizability for metals or precursors that make compoundsemiconductor nanocrystals.

The mixture ratio of the Group 12 metal/precursor to the solvent is in arange of 0.1:1 to 1:100, preferably 0.5:1 to 1:40, and more preferably,1:1 to 1:20.

The concentration of the Group 12 metal precursor solution is in a rangeof 0.001 to 2 M, preferably, 0.005 to 0.5 M, and more preferably, 0.01to 0.1 M.

Next, at least one Group 16 element/precursor is dissolved in acoordinating solvent to obtain a Group 16 element precursor solution.

The Group 16 element may be sulfur (S), selenium (Se), tellurium (Te),or an alloy thereof. The Group 16 precursor may be S powders, Sepowders, Te powders, trimethylsilyl sulfur (S(TMS)), trimethylsilylselenium (Se(TMS)), or trimethylsilyl tellurium (Te(TMS)).

The solvent may be the same solvent as used in the preparation of theGroup 12 metal precursor solution that can coordinate with the Group 16element/precursor. Among examples of the solvent used in the preparationof the Group 12 metal precursor solution, the alkane, the alkene, andthe alkyne hardly coordinate with the Group 16 element/precursor, andthe alkyl amine, the alkyl phosphonic acid, the nitrogen-containinghetero ring, and the sulfur-containing hetero ring slightly coordinatewith the Group 16 element/precursor.

The mixture ratio of the Group 16 element/precursor to the solvent is ina range of 0.1:1 to 1:100, preferably 0.5:1 to 1:40, and more preferably1:1 to 1:20.

The concentration of the Group 16 element precursor solution is in arange of 0.001 to 2 M, preferably 0.01 to 0.5 M. If the concentration ofthe Group 16 element precursor solution is less than 0.01 M, separationof nanocrystals from a reaction solution may be difficult. On the otherhand, if it exceeds 0.5M, the nanocrystals may have a broad sizedistribution.

The Group 16 element precursor solution and the Group 12 metal precursorsolution are mixed and reacted so that crystal growth occurs to therebyobtain Group 12-16 compound semiconductor nanocrystals.

The Group 16 element precursor solution containing two or more Group 16elements/precursors may be added to the Group 12 metal precursorsolution as the following two methods.

In a first method, two or more Group 16 element precursor solutionscontaining the two or more Group 16 elements/precursors are added to theGroup 12 metal precursor solution at a time.

In a second method, two or more Group 16 element precursor solutionscontaining the two or more Group 16 elements/precursors are sequentiallyadded to the Group 12 metal precursor solution.

According to the first method, there can be obtained alloy typemulti-component (three or more components) semiconductor nanocrystalscomprised of at least one Group 12 metal and two or more Group 16elements and having. In the semiconductor nanocrystals, core portion andshell portion have same structure. Examples of the compoundsemiconductor nanocrystals include ZnSSe, ZnSeTe, ZnSTe, CdSSe, CdSeTe,CdSTe, HgSSe, HgSeTe, HgSTe, ZnCdS, ZnCdSe, ZnCdTe, ZnHgS, ZnHgSe,ZnHgTe, CdHgS, CdHgSe, CdHgTe, ZnCdSSe, ZnHgSSe, ZnCdSeTe, ZnHgSeTe,CdHgSSe, and CdHgSeTe. These three or more component compoundsemiconductor nanocrystals can have an appropriate bandgap by adjustingthe ratio of the precursors used, unlike core-shell quantum structuresas will be described later. In particular, a luminance efficiencyincreases only at a specific ratio of the precursors.

According to the second method, first added Group 12 metal and two ormore Group 16 elements are formed core portion, and then added Group 12metal and two or more Group 16 elements are formed shell portion, sothat CdSe/CdS, CdTe/CdS, CdS/CdSe, CdS/CdTe, ZnSe/ZnS, ZnTe/ZnS,ZnS/ZnSe, ZnS/ZnTe, or ZnSe/ZnS core/shell semiconductor nanocrystalscan be obtained.

The heating temperature for obtaining the Group 12 metal precursorsolution is in a range of 100 to 400° C., preferably, 200 to 350° C.,and more preferably, 300 to 350° C. If the heating temperature is lessthan 100° C., crystal grown may be difficult. On the other hand, if itexceeds 400° C., selection of a stable solvent and control of crystalgrowth rate may be difficult.

Crystal growth from a mixture of the Group 12 metal precursor solutionand the Group 16 element precursor solution lasts for 1 second to 10hours, preferably, 10 seconds to 5 hours, and more preferably, 30seconds to 2 hours. If the duration of the crystal growth is outside therange, control of a reaction rate may be difficult.

The Group 12 metal precursor solution containing one or more Group 12metals/precursors may be mixed with the Group 16 element precursorsolution as the following two methods.

In a first method, one or more Group 12 metal precursor solutionscontaining the one or more Group 12 metals/precursors are sequentiallymixed with the Group 16 element precursor solution.

In a second method, one or more Group 12 metal precursor solutionscontaining the one or more Group 12 metals/precursors are mixed with theGroup 16 element precursor solution at a time.

The quantum structures of the semiconductor nanocrystals thus preparedare not particularly limited and may be in shapes of spheres, rods,tripods, tetrapods, cubes, boxes, or stars.

Three or more component compound semiconductor nanocrystals preparedaccording to a method of the present invention have a luminancewavelength region of 300 to 1,300 nm, and a luminance efficiency of 30%or more, preferably 50% or more.

As seen from the fact that FWHM of PL spectrum that represents a sizedistribution of quantum structures is 50 nm or less, preferably 30 nm orless, the three or more component compound semiconductor nanocrystalsare nanoparticles with a uniform size distribution.

Meanwhile, three or more component alloy type semiconductor nanocrystalscomprised of at least one Group 12 metal and one or more Group 16elements and having indecomposable core-shell structures can be widelyused in the fields of displays, sensors, and energies. In particular,the three or more component semiconductor nanocrystals are useful information of an organic film, in particular, a light emission layer ofan organic EL device. These semiconductor nanocrystals may beincorporated in a light emission layer by vapor deposition, sputtering,printing, coating, ink-jet, or e-beam. The thickness of an organic filmmay be in a range of 50 to 100 nm. The organic film as used hereinindicates a film made of an organic compound that is interposed betweena pair of electrodes in an organic EL device and includes an electrontransport layer, a hole transport layer, and the like, except the lightemission layer.

Such an organic EL device may be formed with a commonly knownnon-limiting structure of anode/light emission layer/cathode,anode/buffer layer/light emission layer/cathode, anode/hole transportlayer/light emission layer/cathode, anode/buffer layer/hole transportlayer/light emission layer/cathode, anode/buffer layer/hole transportlayer/light emission layer/electron transport layer/cathode, oranode/buffer layer/hole transport layer/light emission layer/holeblocking layer/cathode.

The buffer layer may be made of a commonly used material, preferably,copper phthalocyanine, polythiophene, polyaniline, polyacetylene,polypyrrole, polyphenylene vinylene, or a derivative thereof, but is notlimited thereto.

The hole transport layer may be made of a commonly used material,preferably, polytriphenylamine, but is not limited thereto.

The electron transport layer may be made of a commonly used material,preferably, polyoxadiazole, but is not limited thereto.

The hole blocking layer may be made of a commonly used material,preferably, LiF, BaF₂, or MgF₂, but is not limited thereto.

An organic EL device of the present invention can be manufacturedaccording to a common method using a light emission material withoutusing a particular apparatus or method.

Hereinafter, the present invention will be described more specificallyby Examples. However, the following Examples are provided only forillustrations and thus the present invention is not limited to or bythem.

EXAMPLE 1 Preparation of CdSeS Nanocrystals

16 g of tri-octyl amine (referred to as TOA, hereinafter), 0.5 g ofoleic acid, and 0.4 mmol of CdO were simultaneously placed in a 100 mlflask provided with a reflux condenser and stirred at 300° C. to obtaina Cd precursor solution.

Separately, Se powders were dissolved in tri-octyl phosphine (referredto as TOP, hereinafter) to obtain a Se-TOP complex solution with a Seconcentration of about 0.1M. S powders were dissolved on TOP to obtainS-TOP complex solution with a S concentration of about 4M.

0.5 ml of S-TOP complex solution 0.5 ml of the Se-TOP complex solutionwere rapidly added to the Cd precursor solution and stirred for about 4minutes.

When the reaction of the resultant mixture was terminated, the reactiontemperature was rapidly reduced to room temperature and thencentrifugation was performed with addition of an ethanol as anon-solvent. A supernatant was decanted and discarded. A precipitate wasdispersed in a toluene and then a PL spectrum in the solution wasmeasured.

The PL spectrum showed an emission wavelength of about 580 nm and FWHMof about 30 nm.

FIG. 1 shows a high-resolution TEM image of the CdSeS nanocrystals thusobtained. As shown in FIG. 1, the nanocrystals exhibited uniform shapesand sizes.

FIG. 2 shows a STEM/EDS image (scale bar=50 nm) of the CdSeSnanocrystals thus obtained. As shown in FIG. 2, the nanocrystalsexhibited uniform composition and size distribution.

FIG. 3 shows a X-ray diffraction spectrum of the CdSeS nanocrystals thusobtained. As shown in FIG. 3, diffraction patterns of CdSe or CdScrystals were observed.

FIG. 4 shows an ultraviolet absorption spectrum of the CdSeSnanocrystals thus obtained. FIG. 4 shows that the CdSeS nanocrystals areuniform nanocrystals excited by a specific energy.

EXAMPLE 2 Preparation of ZnCdSe Nanocrystals

16 g of TOA, 0.5 g of oleic acid, 0.2 mmol of zinc acetyl acetonate, and0.2 mmol of cadmium (Cd) oxide were simultaneously placed in a 100 mlflask provided with a reflux condenser and stirred at 300° C. to obtaina Zn and Cd precursor solution.

Separately, Se powders were dissolved in TOP to obtain a Se-TOP complexsolution with a Se concentration of about 0.25M. 1 ml of the Se-TOPcomplex solution was rapidly added to the Zn and Cd precursor solutionand stirred for about 2 minutes.

When the reaction of the resultant mixture was terminated, the reactiontemperature was rapidly reduced to room temperature and thencentrifugation was performed with addition of an ethanol as anon-solvent. A supernatant was decanted and discarded. A precipitate wasdispersed in a toluene and then a PL spectrum in the solution wasmeasured.

The PL spectrum showed an emission wavelength of about 456 nm and FWHMof about 26 nm.

EXAMPLE 3 Preparation of CdSe/CdS Nanocrystals

16 g of TOA, 0.5 g of oleic acid, and 0.4 mmol of cadmium acetate weresimultaneously placed in a 100 ml flask provided with a reflux condenserand stirred at 300° C. to obtain a Cd precursor solution.

Separately, Se powders were dissolved in TOP to obtain a Se-TOP complexsolution with a Se concentration of about 0.25M. 1 ml of the Se-TOPcomplex solution was rapidly added to the Cd precursor solution andstirred for about 4 minutes.

S powders were dissolved in TOP to obtain a S-TOP complex solution witha S concentration of about 2 M. 1 ml of the S-TOP complex solution wasdropwise added to the CdSe-containing solution and stirred.

When the reaction of the resultant mixture was terminated, the reactiontemperature was rapidly reduced to room temperature and thencentrifugation was performed with addition of an ethanol as a nonsolvent. A supernatant was decanted and discarded. A precipitate wasdispersed in a toluene and then a PL spectrum in the solution wasmeasured.

The PL spectrum showed an emission wavelength of about 520 nm and FWHMof about 30 nm.

FIG. 5 is a photoluminescence (PL) spectrum of the CdSeS nanocrystals,ZnCdSe nanocrystals, and CdSe/CdS nanocrystals according to Examples 1-3of the present invention. FIG. 5 shows the energy level, sizedistribution, and luminance efficiency of the crystals.

EXAMPLE 4 Fabrication of Organic EL Device Using CdSeS Nanocrystals

This Example shows fabrication of an organic EL device using the CdSeSnanocrystals according to Example 1 as a light emission material for theorganic EL device.

A mixture (1:1, by weight) of the CdSeS nanocrystals and a solution ofchloroform of 1 wt % TPD(N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine)was spin-coated on a patterned ITO substrate and dried to form a lightemission layer with a thickness of 40 nm.

Alq3 (tris-(8-hydroxyquinoline) aluminum) was deposited on the lightemission layer to form an electron transport layer with a thickness of40 nm. Then, Mg and Ag were at a time deposited at an atomic ratio of10:1 on the electron transport layer to form a cathode with a thicknessof 75 nm. This completed the organic EL device.

The EL spectrum of the organic EL device showed an emission wavelengthof about 520 nm, FWHM of about 40 nm, brightness of 15 Cd/m², andluminance efficiency of 0.5%. FIG. 6 shows the EL spectrum of theorganic EL device according to Example 4.

As apparent from the above descriptions, a chemical wet method accordingto the present invention provides Group 12-16 compound semiconductornanocrystals which are stable and have high quantum efficiency anduniform sizes and shapes. Furthermore, one or more Group 12metals/precursors and one or more group 16 elements/precursors can bemade into semiconductor nanocrystals with three or more component alloyor core/shell quantum structures through a one-pot process, whichenables adjustment of a bandgap and increase of a luminance efficiency.The semiconductor nanocrystals thus obtained exhibit excellent luminanceefficiency at an emission wavelength of 300 to 1,300 nm.

The semiconductor nanocrystals of the present invention can be widelyused in the fields of displays, sensors, and energies, in particular, information of an organic film such as a light emission layer of anorganic EL device.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A method for preparing semiconductor nanocrystals comprising: (a)mixing one or more Group 12 metals or Group 12 precursors with adispersing agent and a solvent followed by heating to obtain a Group 12metal precursor solution; (b) dissolving one or more Group 16 elementsor Group 16 precursors in a coordinating solvent to obtain a Group 16element precursor solution; and (c) mixing the Group 12 metal precursorssolution and the Group 16 element precursors solution to form a mixture,and then reacting the mixture to grow the semiconductor nanocrystals. 2.The method of claim 1, wherein when the Group 16 elements or the Group16 precursors of step (b) is composed of two or more species, the Group16 element precursor solution of step (c) is composed of two or moresolutions, and the two or more solutions are added to the Group 12 metalprecursor solution, in sequence or at a time.
 3. The method of claim 1,wherein the Group 12 metal is Zn, Cd, Hg, or a mixture thereof.
 4. Themethod of claim 1, wherein the Group 12 metal precursor is zinc acetate,zinc acetylacetonate, zinc iodide, zinc bromide, zinc chloride, zincfluoride, zinc carbonate, zinc cyanide, zinc nitrate, zinc oxide, zincperoxide, zinc perchlorate, zinc sulfate, cadmium acetate, cadmiumacetylacetonate, cadmium iodide, cadmium bromide, cadmium chloride,cadmium fluoride, cadmium carbonate, cadmium nitrate, cadmium oxide,cadmium perchlorate, cadmium phosphide, cadmium sulfate, mercuryacetate, mercury iodide, mercury bromide, mercury chloride, mercuryfluoride, mercury cyanide, mercury nitrate, mercury oxide, mercuryperchlorate, mercury sulfate, or a mixture thereof.
 5. The method ofclaim 1, wherein the dispersing agent is one or more selected from thegroup consisting of an alkylcarboxylic acid having from 2 to 18 carbonatoms, an alkenylcarboxylic acid having from 2 to 18 carbon atoms, analkylsulfonic acid having from 2 to 18 carbon atoms, an alkenylsulfonicacid having from 2 to 18 carbon atoms, an alkylamine having from 2 to 18carbon atoms, and an alkenylamine having from 2 to 18 carbon atoms. 6.The method of claim 5, wherein the dispersing agent is one or moreselected from the group consisting of oleic acid, stearic acid, palmiticacid, hexyl phophonic acid, n-octyl phosphonic acid, tetradecylphosphonic acid, octadecyl phosphonic acid, n-octyl amine, andhexyldecyl amine.
 7. The method of claim 1, wherein in step (a), themolar ratio of the Group 12 metal or the Group 12 metal precursor to thedispersing agent is in a range of 1:0.1 to 1:100.
 8. The method of claim1, wherein the solvent of steps (a) and (b) is one or more selected fromthe group consisting of a primary alkyl amine, a secondary alkyl amine,a tertiary alkyl amine, a nitrogen-containing hetero ring compound, asulfur-containing hetero ring compound, alkane of 6-22 carbon atoms,alkene of 6-22 carbon atoms, and alkyne of 6-22 carbon atoms.
 9. Themethod of claim 8, wherein the solvent is one or more selected from thegroup consisting of trioctylamine, dodecylamine, hexadecylamine,dimethyldodecylamine, and octadecene.
 10. The method of claim 1, whereinthe concentration of the Group 12 metal precursor solution is in a rangeof 0.001 to 2 M.
 11. The method of claim 1, wherein the heating of step(a) is carried out at a temperature of 100 to 400° C.
 12. The method ofclaim 1, wherein the Group 16 element is S, Se, Te, or an alloy thereof.13. The method of claim 1, wherein the Group 16 precursor is sulfurpowders, selenium powders, tellurium powders, trimethylsilyl sulfur(S(TMS)), trimethylsilyl selenium (Se(TMS)), or trimethylsilyl tellurium(Te(TMS)).
 14. The method of claim 1, wherein the concentration of theGroup 16 precursor solution is in a range of 0.001 to 2 M.
 15. Themethod of claim 1, wherein in step (b), the molar ratio of the Group 16element or the Group 16 precursor to the solvent is in a range of 0.1:1to 1:100.
 16. The method of claim 1, wherein the mixing of step (c) iscarried out at a temperature of 50 to 400° C.
 17. The method of claim 1,wherein the crystal growth of step (c) lasts for 1 second to 10 hours.18. Semiconductor nanocrystals having three or more component alloyquantum structures comprised of one or more Group 12 metals and one ormore Group 16 elements.
 19. The semiconductor nanocrystals of claim 18,which are ZnSSe, ZnSeTe, ZnSTe, CdSSe, CdSeTe, CdSTe, HgSSe, HgSeTe,HgSTe, ZnCdS, ZnCdSe, ZnCdTe, ZnHgS, ZnHgSe, ZnHgTe, CdHgS, CdHgSe,CdHgTe, ZnCdSSe, ZnHgSSe, ZnCdSeTe, ZnHgSeTe, CdHgSSe, or CdHgSeTe. 20.The semiconductor nanocrystals of claim 18, wherein the quantumstructures are in shapes of spheres, rods, tripods, tetrapods, cubes,boxes, or stars.
 21. An organic electroluminescent device comprising anorganic film interposed between a pair of electrodes, the organic filmcomprising the semiconductor nanocrystals of claim
 18. 22. The organicelectroluminescent device of claim 21, wherein the semiconductornanocrystals are ZnSSe, ZnSeTe, ZnSTe, CdSSe, CdSeTe, CdSTe, HgSSe,HgSeTe, HgSTe, ZnCdS, ZnCdSe, ZnCdTe, ZnHgS, ZnHgSe, ZnHgTe, CdHgS,CdHgSe, CdHgTe, ZnCdSSe, ZnHgSSe, ZnCdSeTe, ZnHgSeTe, CdHgSSe, orCdHgSeTe.
 23. The organic electroluminescent device of claim 21, whereinthe semiconductor nanocrystals have spherical, rod-like, tripodal,tetrapodal, cubic, box-like, or star quantum structures.